1. Field of the Invention
The present invention relates to electronic devices equipped with a semiconductor device used for electronic equipment, typically mobile equipment requiring impact resistance, such as personal computers; and more particularly to electronic devices that show high drop impact resistance and ease of repair, and their manufacturing methods.
2. Background Art
FIG. 29 is a schematic sectional view of electronic device 551 in which conventional semiconductor device 502 with a ball grid array (hereinafter abbreviated to “BGA”) is connected to mounting board 561. Bump electrodes 505 is formed on one face of semiconductor device 502. FIG. 30 is a schematic sectional view illustrating a state in which mounting board 561 of electronic device 551 is warped. When electronic device 551 is dropped, for example, after being mounted in electronic equipment such as a personal computer, stress is applied to mounting board 561, and mounting board 561 becomes warped. In line with the recent downsizing trend in equipment, bump electrodes 505 are becoming increasingly smaller due to demands for smaller semiconductor devices 502 to be mounted in equipment. If these pieces of equipment are dropped, warping or vibration is generated on mounting board 561 due to impact, and a peel force is applied between bump electrodes 505 and mounting board 561. This increases the risk of causing a crack or peeling on a boundary face between bump electrodes 505 and land (not illustrated) of mounting board 561.
To solve this advantage, Japanese Patent Unexamined Publication No. 2006-100457 proposes electronic device 552 that shows high impact resistance and also enables repair and reworking. More specifically, as shown in FIG. 31A, it proposes electronic device 552 that employs resin consisting of two layers for bonding semiconductor device 502 and mounting board 561. These two layers are layer 571 of peelable and removable resin and layer 572 of resin with high mechanical strength. Using this structure, if semiconductor device 502 needs to be replaced, such as for repair, it can be removed from mounting board 561 by heating peelable resin layer 571 until it becomes fluid.
However, since peelable and removable resin layer 571 is applied between semiconductor device 502 and mounting board 561 in a layer in electronic equipment 552 disclosed in Japanese Patent Unexamined Publication No. 2006-100457, resistance against impact such as drop impact is not sufficient. In addition, it is difficult to remove semiconductor device 502 from mounting board 561 without leaving any residue on mounting board 561, and then to re-connect new semiconductor device 561 immediately after removal in the repair process.
To solve these disadvantages, underfill 573, made of thermosetting resin, is injected in a space between mounting board 561 and semiconductor device 502, as shown in FIG. 31B, and cured so as to bond and fix semiconductor device 502 to mounting board 561. Alternatively, adhesive 574 in the form of thermosetting resin is applied around semiconductor device 502, as shown in FIG. 31C, and cured so as to bond and fix semiconductor device 502 to mounting board 561. If a failure is found in semiconductor device 502 with these structures and repairing is needed, cured underfill 573 or adhesive 574 used needs to be shaved off. This requires many man-hours.
On the other hand, Japanese Patent Unexamined Publication No. 2005-332970 discloses electronic device 555 that uses underfill 575 made of resin composite made by mixing organic thermally expandable particles 576 encapsulating an organic solvent and thermosetting adhesive resin.
In this electronic device 555, as configured above, in the repair process, the organic solvent in organic thermally expandable particles 576 in underfill 575 boils and evaporates on overheating electronic device 555. This changes the hardened resin material into a porous structure that permits semiconductor device 502 to be easily removed from mounting board 561.
However, according to the technology disclosed in Japanese Patent Unexamined Publication No. 2005-332970, microcapsules several micrometers in diameter are dispersed in low-viscosity liquid adhesive. It is thus extremely difficult to uniformly disperse thermally expandable particles 576, due to uneven distribution or sedimentation of microcapsules. In addition, to remove defective semiconductor device 502 from mounting board 561 by increasing the temperature of electronic device 555 to a temperature higher than the expansion temperature of thermally expandable particles 576, separation of semiconductor device 502 occurs at a boundary face of semiconductor device 502 and underfill 575 in addition to the boundary face of mounting board 561 and bump electrodes 505. This is because thermally expandable particles 576 are dispersed in the adhesive. In this case, a large portion of underfill 575 remains on mounting board 561 after removing semiconductor device 502, requiring many man-hours for removing this resin residue.